Matching device for magic tee



Sept. 30, 1958 J. F. ZALESKI MATCHING DEVICE FOR MAGIC TEE 2 Sheets-Sheet 1 Filed Jan. 29, 1954 INVENTOR. \JOHN F'- ZALESKI ATTO E.

P 30, 1958 J. F. ZA LESK| 2,854,637

MATCHING DEVICE FOR MAGIC TEE Filed Jan. 29, 1954 2 Sheets-Sheet 2 INVENTOR. JOHN F. ZALESK\ WWI/W2? ATTORNEY United States Patent MATCHING DEVICE FOR MAGIC TEE John F. Zalesln', Valhalla, N. Y., assignor to General Precision Laboratory Incorporated, a corporation of 'New York Application January 29, 1954, Serial No. 407,071

18 Claims. (Cl. 333-11) This invention relates to a waveguide hybrid junction, or magic tee, in which the series and shunt arms have a common axis.

Hybrid junctions consisting of series and shunt arms in combination are well known and widely used. The more usual form comprises a series arm joined to a broad side of the collinear arms and a shunt arm joined to a narrow side of the collinear arms. There has recently come into use a form in which the series arm is joined to one broad side of the collinear arms, as before, while the shunt arm is joined to the other broad side of the collinear arms. The latter form requires the use of an element of some sort to twist the field in order to obtain coupling between the shunt and the collinear arms. Both forms require, in practical embodiments, one or more elements to compensate for the geometrical discontinuities and impedance mismatches of both the shunt and series arms. Heretofore at least two elements have been required, one for matching the series arm to the junction and one for matching the shunt arm to the junction.

.It is an object of this invention to construct a hybrid junction in which a single element serves to match both the shunt and series arms to the junction.

' Another object of the invention is to provide a hybrid junction having coaxial shunt and series arms.

Another object of the invention is to provide a hybrid junction having coaxial shunt and series arms and in which a single element serves to couple the shunt and collinear arms to match the shunt arm to the junction, and to match the series arm to the junction.

Another object of the invention is to provide a single matching element for a hybrid junction which can be readily adjusted.

Another object of the invention is to provide a hybrid junction which can be manufactured easily.

In accordance with one embodiment of the invention, the waveguide section comprising the collinear arms has a series arm joined to one broad side in the usual manner. The shunt arm is joined to the opposite broad side of the collinear arms. The shunt and series arms are coaxial, and the broad sides of the series arm lie in planes parallel to the planes containing the narrow sides of the shunt arm. Matching and coupling are secured by means of a circular segment shaped element inserted through a slot in the collinear arms. The element may be parallel to the broad sides of the collinear arms and inserted through a slot in a narrow side or may make an acute angle with the broad sides and be inserted through a slot in that broad side to which the shunt arm is secured. In either case, when the element is properly dimensioned and positioned, it will couple the shunt arm to the collinear arms and simultaneously match both the series and shunt arms to the junction.

For a complete understanding of the invention, reference may be made to the accompanying drawing in which:

Figure l is an isometric view of a hybrid junction ac- 'ice portions broken away 'to Figures 3 and 4 are modified and enlarged cross sectional views, similar to Figure 2, useful in explaining the operation of the invention;

Figure 5 is an isometric view of another embodiment of the invention;

Figure 6 is an isometric view of a third embodiment of the invention;

Figure 7 is a cross sectional view taken along the plane 7-7 of Fig. 6; and

Figure 8 is an isometric view of a fourth embodiment.

of the'invention.

Referring first to Fig. 1, there is shown a cruciform shaped hybrid junction, or magic tee, according to the invention. The tee comprises a straight section of rec-' tangular waveguide 11, opposite ends 12 and 13 of which form the collinear arms. A rectangular waveguide arm 14 is secured to one broad side of the section 11 with the broad sides of arm 14 perpendicular to the broad sides of arms 12 and 13 and the narrow sides of arm 14 coplanar with the narrow sides of arms 12 and 13. The junction of arm 14 with arms 12 and 13 as above described comprises a series, or E plane, junction.

A rectangular waveguide arm 15 is secured to the other broad side of the section 11, opposite to the arm 14, the axes of arms 14 and 15' coinciding. The broad sides of the arm 15 lie in planes parallel to the planes of the narrow sides of the arms 12 and 13. That is, the longer cross sectional dimension of the arm 15 is parallel to the axis of arms 12 and 13. As will be more fully explained,

plane, junction with the arms 12 and 13.

Disregarding for a moment the shunt arm 15, the arms 12, 13 and 14 as so far described comprise an E plane junction. Microwave power introduced through the arm 14 will divide equally between arms 12 and 13. However, a compensating element of some sort must be provided if the reflection of large amounts of power back into the arm 14 are to be avoided. In the past, E plane junctions have been compensated by various arrangements such as irises and posts.

Disregarding now for the moment the arm 14, the arms 12, 13 and 15 can be made to constitute an H plane junction. As so far described, there is no coupling between arm 15 and either arm 12 or 13, so that power introduced through arm 15 would not be propagated through arms 12 and 13. It is necessary to provide an element for twisting the microwave field, to provide coupling and for matching the geometrical and impedance discontinuities caused by the junction. The field could be twisted by means of a rod, as described in my copending application Serial No. 264,093 filed December 29, 1951, for Wave Guide Direction Changer, now Patent Number 2,754,483, or, in the case of a cruciform T, the field could be twisted and the discontinuities compensated for by means of a thin conductive member as described in my copending application Serial No. 392,643, filed one broad side of the arms 12 and 13 adjacent to its junction with a broad side of arm 15, so as to make an acute angle with the side containing the slot. If this angle is 45, the plane of the plate will include the axis I of the arms 12 and 13. When the plate 16 is properly dimensioned and inserted the correct distance, both the series arm 14 and the shunt arm 15 will be properly matched. As. an example, a junction was constructedaocording to Figs. 1 and 2 from standard rectangular "waveguide having inside dimensions of 0.4 x 0.9 inch. The plate 16 was made of sheet copper f thick and cut in the shape of a segment ofa circle approximately 1" in radius. The plate was inserted at an angle of 45 through the slot 18 at a distance of approximately 0.4inch, as indicated at d in Fig. 2. This arrangement was found to be substantially matched at 9,000 mc. withthe input applied to either the series arm.14'or the shunt arm, 15.

To understand how the plate 16 matches the arm 14 to the. junction,let us consider microwave energy propagated through the arm 14 in the dominant TE mode. toward the junction. In the absence ofany compensating element in the junction, the wave would see the characteristic pedance of arms 12 and 13 in series, which: is:twice' the characteristic impedance of the arm 14; This large characteristic impedance could be reduced by building up the bottom of the arms 12 and 13 so as to reduce the smaller, or b, dimension. A similar effect could be obtained by inserting a thin plate through a longitudinal slot inthe bottom of arms 12 and 13, as'described and claimed inthe aforementioned copending: application Serial No. 392,643. Test results have shown that moving this thin arcuate plate off center, or even passing it throughthe narrow wall, produces the same electrical effects. The plate 16 thus. decreases the impedance seen by the arm 14,.and is curved so. as to make a gradualtransition to the normal impedance of arms 12 and 13.

To understandhow the plate 16 couples the arm 15 to the arms Hand 13, let usconsider microwave energy propagated in the dominant TE mode through arm 15 toward the junction. The electric force at a certain instant is represented by the vector 21 of Figure 3, which is a cross sectional view of a junction with no compensating element. The vector 21 may be resolved into-two orthogonal components 22 and 23, each at an angle of 45 to the vector 21. The component 22 can be further resolved into a vertical component 24 and'a horizontal component 25, while the component 23 may be further're solved into a vertical component 26 and a horizontal component 27. It can beseen that the two vertical com ponents 24 and.26 are 180 out of phase, so that no wave energy from arm 15 can be propagated'in arms 12 and. 13. If some way could be found to reverse the phase of com ponent 23 Without affecting the component 22, wave energy could be coupled from the arm 15 to the arms 12 and 13.

Figure 4 is a view similar to Fig. 3, but including the plate 16. As in Fig. 3, the vector 21 represents the electric force at a certain instant, and may be resolved into two orthogonal components 22 and 28. The component 22 may, as before be resolved into vertical and horizontal components 24 and 25 respectively. It will be noticed that the component 28 has been reversed in phase, as compared to component 23 of Fig. 3, bythe presence of the plate 16. The resolution of component 28 into vertical and horizontal components 29 and 31 respectively shows that the vertical component 29 is now in phase with the.

vertical component 24, so that wave energy from arm 15 is coupled'to the arms 12 and 13, in the same phase. This phase matching of the vertical components 24 and 29 is accompanied by an. impedance match, as seen by wave energy in the arm15. The curved edge 17 provides a gradualtransitionto. the normal impedance of the arms 12 and- 13.

Referring now toFig, 5, there is shown. a cruciform junction. identical to that shown in Fig. 1 except for thecompensating element. It has been found that matching.may also be obtained by means of a stiff conductive rod.3.3.curved into theposition occupied by the edge 17 of the plate 16. The operation is the same as that described in connection with Figs. 1 and 2.

A matched junction may also be constructed with a plate positioned as shown in Figs. 6 and 7. The arms 12, 13, 14 and 15 of the junction are the same as shown in Fig. l. A slot 36 is cut inone narrow side of arms 12 and 13 midway between and parallel to the broad sides. A plate 37, which is preferably in the shape of a segment of a circle, and having an edge 38, is inserted through the slot 18 parallel to the broad sides. If the plate 37 is properly dimensioned and properly placed, both the series arm 14 and the shunt arm 15 will be properly matched.

The embodiment of the invention illustrated in Figs. 6 and 7 operates in much the same manner as the embodiment of Figs. 1 and 2. The plate 37 decreases the combined impedance of the arms 12 and 13 as seen by wave energy in the arm 14. Reference to Fig. 3 will show how one componentof the electric field from arm 15 is reversed in phase. The plate 37 is-parallel to the horizontal components 25 and 27, but, since it is at the left side as shown in- Figs. 6 and 7, itwill affect the component 25 much more than thecomponent 27. The component 25; is reversed in phase, and this phase reversal causes both of the components 22 and 24 to reverse also. The reversed component- 24 will therefore be in phase with the'component 26, sothat energy from the arm 15 is coupled to. the arms 12 and 13. The electrical effect of the plate 37 Fig. 8 wherein there is shown a rod 39 curved to fit the position occupied by the edge 38 of the plate 37 of Fig. 6'. Operation is substantially the same as that of Fig. 6..

A. junction made in accordance with the inventionhas many advantages. In some cases, the shape alone of the cruciform T makes it more convenient than a conventional magic tee. The necessity for but a single compensating element simplifies the construction of the junction. The slot construction makes for easy adjustment for operation over a wide range of design center frequencies. To change the frequency, it is only necessary to adjust the depthof penetration of the plate or rod.

What is claimed is:

1. A matched cruciform shaped hybrid junction comprising, a straight section ofrectangular waveguide, an

E plane arm joined orthogonally to one broad side of said section, an H plane arm coaxial with said E plane arm joined orthogonally to the other broadside. of said section, and an arcuate conductive element within said junction secured to one side of said section, the plane of said element intersecting the plane of a narrow side of said section in a line parallel to the axis of said section.

2. Apparatus according to claim 1 in which the plane of said element encompasses the axis of said section.

3. Apparatusaccording to claim 1 in which said arcuate element is a conductive rod.

4. Apparatus according to claim 1 in which said element is a conductive plate.

5. A matched cruciform shaped hybrid junction comprising, a straight section of rectangular Waveguide, an

E plane arm orthogonally joined to one broad side of said section, an H plane arm coaxial with said E plane arm orthogonally. joined to the other broad side of said section, and an arcuate conductive element within said'junction secured to one side of said section, the plane of said element encompassingthe axis of said section.

6. A matched cruciform shaped waveguide hybrid junction comprising, a straight section of rectangular,

Waveguide the opposite ends of which form first and second arms of said junction, a third rectangular waveguide arm orthogonally joined to one broad face of said section at the longitudinal midpoint thereof to form an E plane junction therewith, a fourth rectangular waveguide arm orthogonally joined to the other broad side of said section with its longer cross sectional dimension extending along the length thereof and its axis coincident with the axis of said third arm, and an arcuate conductive element within said jrnction secured to one side of said section, the plane of said element intersecting the plane of a narrow side of said section in a line parallel to the axis of said section.

7. Apparatus according to claim 6 in which the plane of said element encompasses the axis of said section.

8. Apparatus according to claim 7 in which said arcuate element is a conductive rod shaped to define an arc of a circle.

9. Apparatus according to claim 7 in which said arcuate element is a thin conductive plate in the form of a segment of a circle.

10. A matched waveguide hybrid junction comprising, a straight section of rectangular waveguide the opposite ends of which form first and second arms of said junction, a third rectangular waveguide arm orthogonally joined to one broad side of said section to form an E plane junction therewith, a fourth rectangular waveguide arm orthogonally joined to the other broad side of said section with its longer cross sectional dimension extending along the length thereof and its axis coincident with the axis of said third arm whereby the axes of all four of said arms intersect at a common point in the center of said junction, and a circular segmentally shaped plate protruding through a slot in one side of said section into the interior of said junction toward said common point of said junction.

11. A matched cruciform shaped hybrid junction comprising, a straight section of rectangular waveguide, an E plane arm orthogonally joined to one broad side of said section, an H plane arm coaxial with said E plane arm orthogonally joined to the other broad side of said section, and an arcuate conductive element within said junction secured to a narrow side of said section midway between the broad sides of said section, said element lying in a plane parallel to said broad sides.

12. Apparatus according to claim 11 in which said element is a conductive rod shaped to form an arc of a circle.

13. Apparatus according to claim 11 in which said element is a thin conductive plate in the form of a segment of a circle, secured to the edges of a slot in said narrow side of said section.

14. A matched waveguide hybrid junction comprising, a straight section of rectangular waveguide the opposite ends of which form first and second arms of said junction, a third rectangular waveguide arm orthogonally joined to one broad side of said section to form an E plane junction therewith, a fourth rectangular waveguide arm orthogonally joined to the other broad side of said section with its longer cross sectional dimension exwith the axis of said third arm, whereby the axes of all four of said arms intersect at a common point in the center of said junction, and a conductive plate in the form of a segment of a circle within said junction secured to a slot in one narrow side of said straight section and lying in a plane midway between and parallel to the broad sides of said straight section.

15. A matched cruciform shaped hybrid junction comprising, a straight section of rectangular waveguide, an E plane arm orthogonally joined to one broad side of said section, an H plane arm coaxially with said E plane arm orthogonally joined to the other broad side of said section, and an arcuate element within said junction secured to a broad side of said straight section, the plane of said element intersecting the plane of a narrow side of said section in a line parallel to the axis of said section.

16. Apparatus according to claim 15 in which said element is a conductive rod formed in an arc of a circle.

17. Apparatus according to claim 15 in which said element is a thin conductive plate in the form of a segment of a circle, secured to the edges of a slot in said broad side of said section.

18. A matched waveguide hybrid junction comprising, a straight section of rectangular waveguide the opposite ends of which form first and second arms of said junction, a third rectangular waveguide arm orthogonally joined to one broad side of said section to form an E plane junction therewith, a fourth rectangular waveguide arm orthogonally joined to the other broad side of said section with its longer cross sectional dimension extending along the length thereof and its axis coincident with the axis of said third arm, whereby the axes of all four of said arms intersect at a common point in the center of said junction, and a thin conductive plate shaped to form a segment of a circle within said junction, secured to a slot in one broad side of said straight section, said slot lying along the junction of said broad side of said section and a broad side of said fourth waveguide arm, the plane of said element encompassing said common point.

References Cited in the file of this patent UNITED STATES PATENTS 2,468,237 Sanders Apr. 26, 1949 2,643,295 Lippman June 23, 1953 2,689,942 Zaleski Sept. 21, 1954 2,758,287 Jacobsen Aug. 7, 1956 FOREIGN PATENTS 678,632 Great Britain Sept. 3, 1952 

